The traditional crane, step by step
The crane is the model everyone starts with and nobody quite finishes perfecting. Here is the sequence I use with a 15 cm square, with notes on the two folds that usually go wrong.
Notes on folding paper
Choosing paper: kami, washi and printer paper
Thin paper holds crisp creases, thick paper forgives mistakes. A short comparison of what is easy to buy and what each sheet is good for.
Valley, mountain, squash
Almost every model is built from a handful of basic folds. Learning to read the dashed and dotted lines in diagrams saves more time than any single trick.